1. Field of the Disclosure
The present disclosure relates in general to valves for mineral recovery wells, and in particular to actuators to actuate valves.
2. Description of Related Art
A gate valve is a valve having a body and a bore through the body. A gate is positioned transverse to the body, and moves linearly to obstruct flow through the bore or allow flow through the bore. Some gates have an aperture that aligns with the bore to allow flow. The gate can be normally open, and thus the gate is closed when it is moved linearly to push the aperture out of alignment with the bore. Alternatively, a gate can be normally closed, and thus the gate is opened when it is moved linearly to position the aperture in alignment with the bore. Regardless of whether the gate is normally open or normally closed, the gate is moved, or actuated, by a valve actuator.
Actuators can be a hydraulic, piston type actuator, or actuators can be a pneumatic piston or diaphragm type actuator. In conventional diaphragm actuators, a diaphragm is moved in response to pressure media, such as gas or other fluids, urging the diaphragm toward the gate valve. The diaphragm is supported by a support plate. When the diaphragm is urged downward with the pressure media, it urges the support plate downward, which then transfers the downward force via a stem to the gate of the gate valve to open or close the gate valve, as applicable.
In some current diaphragm actuators, the outer diameter of the diaphragm support plate does not extend to the inner diameter of the housing in which the diaphragm is positioned so that a portion of the diaphragm hangs over the edge of the support plate and is thus unsupported. As one of skill in the art will appreciate, unsupported regions of a diaphragm are more prone to failure and require a thick and reinforced diaphragm to be able to withstand the force exerted by the pressure media.
In some actuators, an indicator stem protrudes through the cap of the housing of a typical valve actuator. The indicator stem is part of a sealing nut assembly that extends upward from the plate inside the valve actuator housing, or is threadingly connected to the top surface of the plate. The indicator stem sealing nut sealingly engages a bore of the plate. Leaks can occur between the indicator stem sealing nut and the plate. In pneumatic type actuators having a diaphragm, the sealing nut must be removed to replace the diaphragm.
In some cases, the actuator can be manually actuated by pressing against the indicator stem. The force on the stem, however, can damage the stem or internal components of the actuator. It is desirable to be able to externally actuate the valve without exerting forces on the stem that can damage the actuator. It is also desirable to be able to remove and replace the stem without breaking seals between the sealing nut and the plate or diaphragm.